TYPO3 Core

When updating the database reference index after removing an extension that provided a form definition that was referenced in a content element the following PHP error occurrs:

Call to a member function getUid() on null in sysext/form/Classes/Hooks/SoftReferenceParserHook.php

at TYPO3\CMS\Form\Hooks\SoftReferenceParserHook->findRef(
 'tt_content',
 'pi_flexform',
 42,
 'EXT:uninstalled_extension/Configuration/Form/contact.form.yaml',
 'formPersistenceIdentifier',
 '',
 'sDEF/lDEF/settings.persistenceIdentifier/vDEF/'
)

How to reproduce:

1. Install an extension providing a form.yaml
2. Add a form content element and reference that form.yaml
3. Uninstall the extension

Now the following actions will reproduce the issue:

• Edit the form content element, select another form definition and click "ok" in the popup
• Update the database reference index